multistart: check duplicates

* src/symlist.h, src/symlist.c (symbol_list_find_symbol)
(symbol_list_last): New.
(symbol_list_append): Use symbol_list_last.
* src/reader.c (grammar_start_symbols_add): Check and discard duplicates.
* tests/input.at (Duplicate %start symbol): New.
* tests/reduce.at (Bad start symbols): Add the multistart keyword.

1 files changed, 0 insertions, 0 deletions

diff --git a/gnulib b/gnulib
-Subproject 9351b4033bbf0bb1df3d3412376fefe785168c2
+Subproject b141afaf9ba197e361510da075556822ac453ff